Adaptive power supply for telecommunications networks

ABSTRACT

An adaptive power supply span powers devices used in telecommunications. It includes a power circuit and control circuit that receives power and sense signals therefrom and provides a control signal thereto and distinguishes between a first network interface load having a constant voltage input power requirement and a second network interface unit load having a constant current input power requirement. A voltage control circuit and current control circuit are interconnected together and connected to the power circuit. A control signal from the voltage control circuit and current control circuit extends to the power circuit. The control circuit maintains a fixed output voltage for constant voltage regulation for the first network interface unit load, if the output current remains below a threshold current. The circuit limits the output current to a regulated value for constant current regulation below the initial maximum value for powering a second network interface unit if the initial output current is greater than the threshold current for a time greater than a threshold time.

FIELD OF THE INVENTION

The present invention relates to power supplies used in communicationnetworks, and more particularly, the present invention relates to powersupplies used for span powering Network Interface Unit (NIU) loads intelecommunications networks.

BACKGROUND OF THE INVENTION

In some telecommunication networks, span powering is used when a powersupply located at a service provider site, such as a central office,furnishes power to a remote site. Typically, a service providerfurnishes power to equipment at the remote site near the customerpremise from the power supply at the service provider site. In somecommunications networks, a pair of wires, often referred to as thecopper twisted pair, couples both a communications signal and the powersupply energy from the service provider site to the remote site. Inother telecommunications systems, the twisted pair of wires serves onlyas an electrical path for coupling power from the service provider siteto the remote site.

When span powering a remote DS1 device, for example, a DS1 power supplyat the local site furnishes, via the twisted wire pair, a desiredcurrent and voltage to the remote site for powering a DS1 device. Insome applications, it is desired to span power a DS3 NIU located at aremote site from the local site over twisted pair. Because of thedifferences in power requirements between the DS1 and DS3 devices, apower supply capable of powering a DS3 device must be used at the localsite. A DS1 span power supply does not have the appropriate output topower a DS3 device. Hence, for span powering, a local DS1 power supplyis required for a DS1 communications connection and a local DS3 powersupply is required to span power a DS3 NIU. These power supplies are notinterchangeable.

The assignee of the instant application, ADTRAN, Inc., designs andmanufactures a Span Power and Protection Module (SPPM) that receives andisolates up to 28 DS1 signals, combines these signals with isolatedT1-style (60 mA regulated) span power, and couples the combined spanpower/DS1 signal to traditional copper, twisted pair telephone line topower and drive a DS1 Network Interface Unit (DS1 NIU). In this SPPM,the T1 style span power is generated by 28 identical isolated span powersupplies, which regulate their respective output currents to a nominal60 mA, in one non-limiting example. This value is held in conjunctionwith the DS1 network interface units that terminate their span powerinput with a shunt device, for example, a zener diode to define the NIUoperating voltage.

As noted before, the SPPM provides DS1 span power capability, but is notcapable to span power a DS3 NIU. The powering requirements for a DS3 NIUare substantially different than those of a DS1 NIU. DS3 NIUs aretypically powered using a constant voltage instead of constant currentand the current requirements (thus total power requirements) are muchhigher than those of a DS1 NIU.

A possible solution is to change the SPPM so that several of its 28powering ports would be “DS3 only.” This approach, however, suffers thedisadvantages of losing availability from those “DS3 only” ports for themore common DS1 NIU application and could result in the destruction of aDS1 NIU should it be inadvertently connected to a DS3-designatedpowering port. This is unacceptable in practice.

Another possible solution changes the SPPM to incorporate a span powersupply that powers either a DS3 NIU or DS1 NIU using a user-accessibleswitch that allows a user to select a desired mode of operation. Thisswitchable-mode, span power supply would be used in several of the 28ports with the original DS1-only span power supply used in the remainingports. This approach, however, is not automatic and requires direct userintervention. Also, as a further disadvantage, a DS1 NIU could bedestroyed, if the user does not put the mode-select switch in theappropriate position for the equipment to be powered.

SUMMARY OF THE INVENTION

An adaptive power supply span powers devices used in telecommunicationssuch as supplying span power to Network Interface Units (NIU). Theadaptive power supply includes a power circuit, a control circuit, and aline filter and distinguishes between a first network interface loadhaving a constant voltage input power requirement and a second networkinterface unit load having a constant current input power requirementthat is less than the maximum input current required by the firstnetwork interface unit load. A voltage control circuit and currentcontrol circuit are interconnected together and are connected to thepower circuit. A control signal from the voltage and current controlcircuits is connected to the power circuit via a feedback element suchas an optocoupler. The control circuit maintains a fixed output voltage(voltage regulation) to power a first network interface unit load, ifthe output current remains below a threshold current. The controlcircuit limits the output current to a regulated value (currentregulation) for powering a second network interface unit if the initialoutput current is greater than the threshold current for a time greaterthan a threshold time value.

The adaptive power supply also includes a hysteretic current selectcircuit connected to the current control circuit to set a regulatedcurrent value. It includes a comparator circuit that receives areference signal and a current sense signal and compares the signals andoutputs a signal to the current control circuit and reduces the outputcurrent regulation value to a lower level for powering a secondinterface unit load. The voltage and current control circuits are formedas operational amplifier circuits that compare reference signals tosense signals and amplify the difference to output a control signal.

In yet another aspect, a first interface unit load is a DS3 networkinterface unit (NIU) and a second network interface load is a DS1network interface unit (NIU). A line filter can be connected to theoutput of the dual mode power supply for filtering the power output foruse with either first or second network interface unit loads. An opticalcircuit within the power circuit can connect the control circuit to thepower circuit. The power circuit can also be formed as a powertransformer, a modulator and drive circuit, a first regulator circuitthat derives power from the transformer to provide power to themodulator and drive circuit over a wide operating range, a secondregulator circuit that also derives power from the transformer to powerthe control circuit over a wide operating range, and a main power outputfrom the transformer for powering first and second network interfaceunits.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will become apparent from thedetailed description which follows when considered in light of theaccompanying drawings in which:

FIG. 1 is a block diagram showing a communications system thatincorporates an enhanced Span Power and Protection Module (SPPM) at alocal/service site in which the SPPM includes an adaptive power supplythat powers a DS3 or DS1 Network Interface Unit (NIU) load andautomatically determines and applies the appropriate power required bythe NIU load.

FIG. 2 is a graph depicting voltage and current characteristics of theadaptive power supply when furnishing power to a DS3 NIU load inaccordance with a non-limiting aspect.

FIG. 3 is a graph depicting voltage and current characteristics of theadaptive power supply when furnishing power to a DS1 NIU load inaccordance with a non-limiting example.

FIG. 4 is a high-level flowchart depicting a method used for operatingthe communications system and as part of an associated SPPM shown inFIG. 1 in accordance with a non-limiting example.

FIG. 5 is a high-level schematic circuit diagram of an adaptive powersupply that can be used in the communications system and as part of anassociated SPPM shown in FIG. 1 in accordance with a non-limitingexample.

FIG. 6 is a schematic circuit diagram of the automatic identification(ID) feedback and control circuit (control circuit) shown in FIG. 5 andused with the adaptive power supply in accordance with a non-limitingexample.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Different embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsare shown. Many different forms can be set forth and describedembodiments should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope to those skilled in the art. Like numbers refer to like elementsthroughout.

In accordance with non-limiting examples, the adaptive power supplypowers a DS3 or DS1 Network Interface Unit (NIU). The adaptive powersupply automatically determines and applies the proper type of poweringrequired by the network interface unit load. The adaptive power supplyreacts to the response of the two different NIU load types (DS1 or DS3)and adjusts its output accordingly. It is possible to use this dual modepower supply in different ports of the 28 total power supply ports ofthe SPPM and provide a customer full 28 ports of isolated DS1 signalingand power, or provide up to an “n” number of ports of isolated DS3power. The remaining ports would only be available for DS1 signaling andpower. No user intervention would be required and this selection betweenproviding power to a DS1 or DS3 NIU load becomes automatic. In addition,each dual mode power port can be sized to power two DS3 NIU loads.

The adaptive power supply operates as an adaptive span power supply atthe local (or service site) and can provide power to a remote DS1 NIU,or provide power to up to two remote DS3 NIUs, in a non-limitingexample. The delivered voltages and currents provide this power toeither a DS1 or DS3 NIU load without causing harm to either type. Forconventional communication systems having these different types of spanpowering requirements, the adaptive power supply to be described belowis advantageous and overcomes many of the drawbacks identified above.

FIG. 1 is a high-level block diagram of a communications system 10showing a local/service site 12 and a remote site 14. The local/servicesite 12 includes DS1 and/or DS3 transceivers 16 as known to thoseskilled in the art. An enhanced Span Power and Protection Module isillustrated at 20 and includes at least one adaptive power supply 22(typically an “n” number) for powering a DS1 or DS3 NIU and a pluralityof power supplies 24 formed as the standard power supplies for poweringa DS1 NIU. A plurality (or “n” number) of adaptive power supplies 22 aretypically incorporated within the Span Power and Protection Module atvarious ports. In one example, three are used. The adaptive power supply22 has a power output 30 that varies and can be used for powering a DS3NIU or DS1 NIU located at a remote site. For example, the power output30 could be at a voltage and current combination for powering a DS1 NIU34 and output power into a combiner and protection circuit 32, whichalso receives a signal from a DS1 transceiver, combines the power andsignal, and passes the combined power and signal to the DS1 NIU 34 viatwisted wire pair telephone cable 38. In a mode of operation forpowering a DS3 NIU, however, the adaptive power supply 22 outputs powerto a combiner and protection circuit but no DS3 signal is present soonly power is delivered over the twisted pair to the DS3 NIU 36 at theremote site. The DS3 circuit receives communications signals typicallyover a coaxial cable 40 from a DS3 transceiver. The DS3 and DS1 NIUshave different power requirements as indicated above and requiredifferent types of power input.

It should be understood that Digital Signal One (DS1) signalling (alsoknown as a T1 and sometimes a “DS-1” signal) for a T-carrier signallingsystem uses a DS1 frame synchronization to identify different time slotswithin a 24-channel frame as indicated above. Each DS1 circuit is madefrom 24 eight-bit channels as time slots or Digital Signal Zero (DS0)basic digital signalling rate of about 64 Kbit/s corresponding to thecapacity of one voice and frequency equivalent channel. Digital SignalLevel 3 corresponding to DS3 as indicated above equates to 28 T-1 linesfor a total signalling rate of about 1.544 mbps and multiplexed throughan M13 with 188 additional signalling and control bits to each T-3frame. Each frame is transmitted at about 8,000 times a second for atotal T-3 signalling rate of about 44.736 Mbps. Different components asshown in FIG. 1 can be used such as manufactured by ADTRAN, Inc. ofHuntsville, Ala. These components include an enhanced span powerprotection module for 28 transmit and receive DSX-1 facilities. Thisenhanced SPPM module includes at least one adaptive power supply 22 asindicated above for at least one communications port and operable with aDS1 or DS3 network interface unit for demarcation and a loopback pointfor DS1 and DS3 circuits. The network interface units can serve as aninterface between a T1 metallic span and customer premises equipment(CPE) and provide maintenance loopback plus collection and reporting ofDS1 performance statistics. A DS3 network interface unit can respond toDS3 loopback codes.

The span power and protection module protects up to 28 DSX-1 transmitand receive facilities against outside plant lightning and power faultevents. The system can be used with digital subscriber line (DSL)communication systems or other systems known to those skilled in theart.

In accordance with a non-limiting aspect, the characteristics of the twodifferent types of equipment, DS1 NIU or DS3 NIU, to be powered areleveraged. A dual mode control circuit, also termed as an automaticidentification (ID) and feedback and control circuit, takes advantage ofthe differences of the loads required by the DS1 or DS3 NIUs and adjuststhe output of the adaptable power supply for each load type, thusworking as an adaptable span power supply. Details of such circuits areexplained below with reference to FIGS. 5 and 6. FIG. 5 shows theadaptive power supply and the feedback and control circuit (termed alsogenerally as the control circuit) is shown in FIG. 6 at referencenumeral 500 and will be explained in greater detail with reference toFIG. 6 after a more general discussion of the adaptive power supply.

The initial mode of the control circuit 500 is voltage regulation. Inone non-limiting example, the adaptive power supply 22 (FIG. 5) outputis monitored and regulated to a maximum, open-circuit voltage value. Thecontrol circuit 500 maintains this output voltage from zero outputcurrent to a predetermined maximum output current limit (Imax). If theoutput current increases to Imax, the feedback and control circuit 500initially regulates the output current to Imax. In the example circuit,Imax is nominally 600 mA, but can be any value. The control circuit 500also has a current threshold (Ith) that activates a circuit that setsthe output current regulation value as explained in greater detailbelow. Ith must be lower than Imax and is typically 500 mA in theexample circuit. When the load current exceeds Ith for a predeterminedamount of time, the output current regulation value is reduced from Imaxto a lower level, Ireg. In this example circuit, Ireg is about 60 mA,typical of T1 powering circuits, but it can be any value lower than Ith.

When the output of this dual mode adaptive power supply 22 (as a spanpower supply, for example) is connected to one or two DS3 NIUs, the NIUsoperate normally from the regulated 54V output, drawing less currentthan Ith as the current threshold. In this case, the dual mode adaptivepower supply 22 operates as a constant voltage (voltage regulated) powersupply.

A DS1 NIU typically has a shunt, voltage clamp device, for example, azener diode or transient voltage protector, across its span power inputvoltage terminals. This clamping voltage is typically about 20V-30V.When a DS1 NIU is connected to the dual mode adaptive power supply 22 asa span power supply, the shunt voltage clamping device of the DS1 NIUpulls the output current of the span power supply to its maximum currentlimit value Imax. The output voltage falls to the clamp voltage plus thevoltage drop in the resistive distribution lines. After a brief periodof operation at Imax, the hysteretic feature of the feedback and controlcircuit 500 reduces the output current to Ireg. The adaptive powersupply 22 continues its operation as a constant current regulatingsupply. The period of time that the DS1 NIU is operating at Imax insteadof Ireg is brief (<20 ms typically) and well within the safe operatingarea of devices used for a DS1 NIU input voltage clamping. Thus, it ispossible to maintain full product flexibility, i.e., powering either DS3NIUs or a DS1 NIU, without operator intervention, while also reducingany associated reliability risks due to operator error.

FIG. 2 is a graph showing the output voltage, Vo, and current Io of theadaptive power supply 22 when the supply is connected to a remote DS3NIU 36 which is also connected to an associated transceiver. When theadaptive power supply 22 is turned on, a voltage (V_(MAX)) ofapproximately 54 volts, in one embodiment, appears across the outputterminals. For other embodiments, other values for Vmax are possible. Nocurrent flows from the power supply until the twisted pair is connectedto the remote network interface unit, as indicated by time=0. When theadaptive power supply 22 is connected to an NIU over the wire pair,current will flow between the adaptive power supply and the remote siteNIU. When the remote equipment is one or two DS3 NIUs, the currentsupplied by the adaptive power supply 22 will be less than Ith. Sincethe output current Io is less than a threshold current value, I_(TH),then the voltage output of the adaptive power supply remains at V_(MAX)as shown in FIG. 2. In one embodiment, I_(TH) is 500 milliamps. Theremote DS3 power supply, receiving power over the twisted pair, receivesa current of around 300 milliamps at a voltage somewhat less thanV_(MAX) because of the voltage drop on the twisted pair.

FIG. 3 is a graph depicting operation and function when the adaptivepower supply 22 is coupled to a remote DS1 NIU over a twisted wire pair.If the current furnished by the adaptive power supply remains greaterthan I_(TH), as seen in the graph of FIG. 3, for a threshold amount oftime T_(TH) then the output current is limited to and regulated atI_(REG). In one embodiment I_(REG) is equal to around 60 milliamps. Thevalue of 60 milliamps is an example of a typical current value requiredof a remote DS1 NIU. In other embodiments, I_(REG) has other values. Thevoltage across the terminals of the adaptive power supply 22 will dropfrom V_(MAX) to a value that is equal to the voltage across the remoteDS1 NIU plus the voltage drop on the twisted pair. For one embodimentT_(TH) is approximately 20 milliseconds although other values arepossible. The value of T_(TH) is selected to provide sufficient time tocharge the input capacitance of a DS3 NIU without changing the mode ofoperation.

FIG. 4 shows a high-level flowchart of a method of operation andfunction that can be used in accordance with the non-limiting examples.The process begins at 300. After the adaptive power supply 22 is coupledto a remote NIU via the twisted wire pair 38, the adaptive power supply22 is turned on (block 310). Current flows to the remote NIU on thetwisted wire pair. Initially, the control circuit of the adaptive powersupply 22 maintains the output voltage at a value of V_(MAX) and limitsthe output current to I_(MAX) (block 315). The output current, Io, ofthe adaptive power supply may be less than I_(MAX). If the outputcurrent is greater than I_(TH) for a period of time T_(TH), then the YESpath of decision (block 320) is followed. However, if the current doesnot exceed I_(TH), then the adaptive power supply continues outputvoltage regulation (block 315). If the YES path of block 320 is taken,then the adaptive power supply limits the output current to I_(REG),which results in a drop of the output voltage to some value less thanV_(MAX) (block 330). When this state of operation as described by block330 is reached, a DS1 NIU is being powered. If the DS1 NIU isdisconnected, then the current from the adaptive power supply 22 dropsto a small value that is typically less than I_(MIN) and operation ofthe adaptive power supply returns to block 315.

There now follows a description of the adaptive power supply 22 withreference to FIG. 5, which illustrates a simplified schematic circuitdiagram of the adaptive power supply that operates as a dual modeadaptive power supply when used as a span power supply for DS1 or DS3NIUs. Reference numerals for the different components will be given inthe 400 and 500 series.

The dual mode characteristics are implemented by the control circuit 500that is shown in the schematic circuit diagram in FIG. 6 and correspondsto an automatic identification (ID) feedback and control circuit labeledin FIG. 5 at 500. In a non-limiting, preferred embodiment, the adaptivepower supply 22 uses a flyback converter designed for a wide range ofoutputs for the main power stage. The design and implementation of theflyback converter main power stage 420 is well known to those skilled inthe art of power electronics and will not be described herein. Otherembodiments of the main power stage are obvious to those skilled in theart. To accommodate the wide range of output voltages, primary andsecondary side auxiliary voltages are regulated to power the modulatorand drive circuit 414 and control circuit 500. The primary auxiliaryregulator 410 and the secondary auxiliary regulator 412 are formed inone embodiment as linear emitter-follower circuits but can be formed innumerous other circuits well known to those skilled in the art.

As shown in FIG. 5, the main power stage 420 provides power to thecontrol circuit 500 and the main output 406. The main output is coupledto a line filter 450 through a resistor Rcs which is used to sense theoutput current, producing a current sense voltage Current_Sense.Voltage_Sense, which is identically the output voltage Vo of the mainoutput 406, and Current_Sense are connected to the control circuit 500which is shown in FIG. 6 including the schematic connection points forCurrent_Sense and Voltage_Sense. The output of the control circuit 500is a control signal Control that is connected to the main power stage420 to provide voltage and current control of the main output 406. Theoutput of the line filter 450 is the final output of the adaptive powersupply and is connected to the combiner and protection circuit 32 asshown in FIG. 1 where it is joined with a DS1 signal for DS1 applicationand connected to a twisted wire pair 38 for conveyance to a remote NIU34/36. For DS3 application, no signal is presented to the combiner andprotection circuit 32 but power only is connected to a twisted pair forpowering a DS3 NIU.

In a preferred aspect, the control circuit 500 shown in FIG. 6 isimplemented using a quad (four) operational amplifier integrated circuitand a reference voltage circuit, but for clarity, FIG. 6 depictsindividual operational amplifiers.

The voltage control function is implemented with the U1-based circuitshown in FIG. 6. Resistors R1 and R2 divide the main power stage 420output voltage Vo (shown as Voltage_Sense) to compare to the referencevoltage at U1 configured in conjunction with Q1 as a transconductingerror amplifier circuit. The reference voltage (REF) is generated by areference circuit 510 shown in FIG. 6. The reference voltage can begenerated by many different circuits well known those skilled in theart. The error voltage output of U1 is translated to a current by R5 andtransistor Q1. This current and the current drawn by R13/Q2 as describedbelow are joined to form a control signal Control and are connected tothe power circuit via 502 also shown in FIG. 5. Negative feedback for U1comes from the voltage drop made by the current conducting in R6 coupledto the non-inverting terminal of U1 through a compensation networkformed by R4, C1, and C2. The control signal is translated to theprimary of the main power stage and coupled to the modulation and drivecircuit 414 of FIG. 5 via an optical coupler circuit 440 shown in FIG.5. This circuit 440 could be associated with the control circuit 500,but is shown within the main power stage in FIG. 5. If Voltage_Sense isless than the prescribed regulated value, then U1 output voltage isnearly zero and the voltage control function is inactive.

The current control function is implemented with the U2-based circuitshown in FIG. 6. The output current Io of the main output is translatedto a current sense voltage via a current sense resistor Rcs shown inFIG. 5. The current sense voltage is coupled to U2 via R7 and iscompared to the voltage at the inverting terminal of U2, which is theREF signal scaled down by R8 and R10. Transistor Q5 is initially open soR9 does not affect the voltage at the inverting terminal of U2. If theadaptive power supply output current increases to the maximum levelImax, then the U2 output becomes positive and causes transistor Q2 toconduct, adding to the current drawn by Q1. The control signal Controlcomprises the combined currents of R6/Q1 and R13/Q2 and its valuecontrols the output voltage Vo or output current 10 of the main output406.

As the current in R13/Q2 increases, the main power stage output voltagedecreases, and the U1 output decreases until transistor Q1 no longerconducts. At this point, operation has transitioned from constantvoltage regulation to constant current regulation. Negative feedback forU2 is generated by the voltage drop across R13 from the current drawn bytransistor Q2. This voltage drop is coupled to the non-invertingterminal of U2 via the compensation network formed by R11, C4, and C3.

The current sense voltage (Current_Sense) is also used by a hystereticcurrent select circuit that includes an operational amplifier U3(operating as a comparator) and its associated circuit as a hystereticcurrent select function to set the regulated current value. IfCurrent_Sense is greater than the voltage at the inverting terminal ofU3, formed by REF, R18, and R19, for a long enough period of time toovercome the delay presented by R20 and C18, then the output voltage ofU3 will transition high, turning on transistors Q4 and Q5 through theirrespective gate resistors. When transistor Q5 turns on, R9 is switchedinto the inverting terminal circuit of U2, reducing the voltage at theU2 inverting terminal, which reduces the main power stage 420 outputcurrent regulation value to the lower desired level, which in thiscircuit example is the nominal 60 mA value for a DS1 NIU. Turning ontransistor Q4 switches R17 into the U3 inverting terminal circuitreducing the voltage at its inverting terminal so that the outputcurrent Io must be reduced substantially below the lower currentregulation value to change the control circuit operation back to theinitial mode.

When the dual mode span power supply is connected to one or two DS3NIUs, U1 and transistor Q1 are active and the main power stage 420output voltage is regulated at 54V. The output current creates a currentsense voltage that is not high enough to trip U2 or U3, so transistor Q2is inactive and not conducting. When the span power output is connectedto a DS1 NIU, the regulated output voltage is at about 54V in thisexample and is greater than the internal clamp voltage of the DS1 NIU ofabout 20V to about 30V. As a result, the DS1 NIU input clamp pulls thedual mode adaptive power supply into current regulation with theregulation level being the higher initial value Imax (about 600 mA).Imax is greater than the current required to trip the hysteretic currentlevel circuit (Ith), so after the set time delay (typically about 20ms), the U3 output becomes active (goes high), changing the currentregulation level to the lower Ireg (about 60 mA) value suitable for asingle DS1 NIU. When the adaptive span power supply is disconnected fromthe DS1 NIU, the operation of the adaptive power supply will return toits original mode of regulation of the main power stage output voltage.

The illustrated control circuit 500 in FIG. 6 is only one example of acircuit that can be used to implement the new dual mode functionality asdescribed above. A basic algorithm that should be supported in ahardware implementation and applied to different circuits as examples isnow set forth.

As a first step, the open circuit voltage is regulated to a maximumvoltage. As a second step, the output current is monitored and comparedto a maximum value. These first two steps correspond to operatingequipment configured for constant voltage input such as DS3 NIUs. As athird step, if the output current increases to the maximum value, thenoutput current is regulated at that value and the output voltage isdecreased. As a fourth step, if the output current is regulated at themaximum value for a predetermined time, then the regulated current valueis reduced to a lower value with the output voltage being furtherreduced. Steps three and four as described correspond to operatingequipment configured for constant current input such as DS1 NIUs. As afifth step, the output current remains limited to the reduced leveluntil the load is essentially removed.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. An adaptive power supply for span powering in telecommunications,comprising: a power circuit; and a control circuit connected to thepower circuit that receives power, an output voltage sense signal, andan output current sense signal from the power circuit, said controlcircuit configured to generate a control signal to the power circuit andsaid control circuit configured to distinguish between a first networkinterface unit load having a constant voltage input power requirementand a second network interface unit load having a constant current inputpower requirement that is less than the maximum input current requiredof the first network interface unit so the adaptive power supplyselectively delivers a constant voltage output power for a first networkinterface unit load and a constant current output at a level below themaximum output current limit for a second network interface unit load.2. The adaptive power supply according to claim 1, said control circuitcomprises a voltage control circuit configured to generate a voltagecontrol signal and current control circuit configured to generate acurrent control signal, and interconnected together and connected tosaid power circuit and wherein said voltage control signal and currentcontrol signal form together the control signal generated from thecontrol circuit to said power circuit and maintaining a fixed outputvoltage for constant voltage regulation and powering a first networkinterface unit load if the output current remains below a thresholdcurrent and to limit the output current to a regulated value as constantcurrent regulation for powering a second network interface unit if theinitial output current is greater than the threshold current for a timegreater than a threshold time value, and wherein said control circuit isconfigured to increase the power to the power circuit in response to theoutput current reaching a maximum, thus decreasing power from the powercircuit and transitioning from a constant voltage regulation to aconstant current regulation.
 3. The adaptive power supply according toclaim 2, and further comprising a hysteretic current select circuitconnected to said current control circuit that sets a regulated currentvalue and comprising a comparator circuit that receives a referencesignal and the current sense signal.
 4. The adaptive power supplyaccording to claim 1, wherein said voltage control circuit comprises anoperational amplifier circuit that receives a reference signal and thevoltage sense signal and said current control circuit comprises anoperational amplifier circuit that receives a reference signal and thecurrent sense signal.
 5. The adaptive power supply according to claim 1,wherein a first interface unit load comprises a DS3 network interfaceunit load and a second network interface load comprises a DS1 networkinterface unit load.
 6. The adaptive power supply according to claim 1,and further comprising a line filter connected to the output of thepower circuit for filtering the power output for use with either firstor second network interface unit loads.
 7. The adaptive power supplyaccording to claim 1, and further comprising an optical coupler circuitwithin the main power circuit connecting the control circuit to thepower circuit.
 8. The adaptive power supply according to claim 1,wherein said power circuit comprises a power transformer, a modulatorand drive circuit, a first regulator circuit that derives power from thetransformer to provide power to the modulator and drive circuit over awide operating range, a second regulator circuit that also derives powerfrom the transformer to power the control circuit over a wide operatingrange.
 9. A span power and protection module for span powering aplurality of DS1 network interface units and an “n” number of DS3network interface units, comprising: a plurality of DS1 power suppliesthat each provide power to a respective DS1 network interface unit; an“n” number of adaptive power supplies for span powering one of either aDS1 network interface unit or a DS3 network interface unit, eachadaptive power supply comprising: a power circuit; and a control circuitconnected to the power circuit that receives power, an output voltagesense signal, and an output current sense signal from the power circuit,said control circuit configured to generate a control signal to thepower circuit and said control circuit configured to distinguish betweena first network interface unit load having a constant voltage inputpower requirement and a second network interface unit load having aconstant current input power requirement that is less than the maximuminput current required of the first network interface unit so the powercircuit selectively delivers a constant voltage output power for a firstnetwork interface unit load and a constant current output at a levelbelow the maximum output current limit for a second network interfaceunit load.
 10. The span power and protection module according to claim9, wherein said DS1 power supplies and adaptive power supplies withinsaid span power and protection module isolate DS1 signals and combinethe signals for T-1 style regulated span power.
 11. The span power andprotection module according to claim 9, wherein said control circuitcomprises a voltage control circuit configured to generate a voltagecontrol signal and current control circuit configured to generate acurrent control signal and interconnected together and connected to saidpower circuit and wherein said voltage control signal and currentcontrol signal form together the control signal generated from thecontrol circuit to said power circuit and maintaining a fixed outputvoltage for constant voltage regulation and powering a first networkinterface unit load if the output current remains below a thresholdcurrent and to limit the output current to a regulated value as constantcurrent regulation for powering a second network interface unit if theinitial output current is greater than the threshold current for a timegreater than a threshold time value, and wherein said control circuit isconfigured to increase the power to the power circuit in response to theoutput current reaching a maximum, decreasing power from the powercircuit and transitioning from a constant voltage regulation to aconstant current regulation.
 12. The span power and protection moduleaccording to claim 11, and further comprising a hysteretic currentselect circuit within each adaptive power supply and connected to saidcurrent sense control circuit that sets a regulated current value andcomprising a comparator circuit that receives and compares a referencesignal and the current sense signal.
 13. The span power and protectionmodule according to claim 9, wherein said voltage control circuitcomprises an operational amplifier circuit that receives a referencesignal and the voltage sense signal and and said current control circuitcomprises an operational amplifier circuit that receives a referencesignal and the current sense signal.
 14. The span power and protectionmodule according to claim 9, wherein a first network interface unitloads that are connected to an adaptive power supply comprise a DS3network interface unit load and a second network interface unitcomprises a DS1 network interface unit load.
 15. The span power andprotection module according to claim 9, and further comprising a linefilter connected to the output of the power circuit within each adaptivepower supply for filtering the power output for use with either first orsecond network interface unit loads.
 16. The span power and protectionmodule according to claim 9, and further comprising an optical couplercircuit within the power circuit within each adaptive power supply andconnecting the control circuit to the power circuit.
 17. The span powerand protection module according to claim 9, wherein said power circuitcomprises a power transformer, a modulator and drive circuit, a firstregulator circuit that derives power from the transformer to providepower to the modulator and drive circuit over a wide operating range, asecond regulator circuit that also derives power from the transformer topower the control circuit over a wide operating range.
 18. A method ofspan powering either a first network interface unit load having aconstant voltage input power requirement or a second network interfaceunit load having a constant current input power requirement less thanthe maximum required input current of a first network interface unit,which comprises: providing a power circuit and providing a controlcircuit connected to the power circuit that receives power therefrom andincludes a voltage control circuit and current control circuitinterconnected together and connected to said power circuit; sensing acurrent output by the power circuit; comparing the current output with acurrent threshold value; configuring the power circuit and voltagecontrol circuit and current control circuit to operate in a currentlimiting mode when a current threshold value is exceeded for thresholdtime for powering a second network interface unit; and otherwise,maintaining a voltage mode of operation for the power supply when thecurrent remains less than the threshold value for powering a firstnetwork interface unit having a constant voltage input powerrequirement.
 19. The method according to claim 18, which furthercomprises increasing a control current from the voltage control circuitand the current control circuit to the power circuit and decreasingpower from the power circuit and transitioning from a constant voltageregulation to a constant current regulation.
 20. The method according toclaim 18, which further comprises optically coupling control currentfrom the control circuit to the power circuit.